The present invention relates to a connector for receiving and connecting multiple optical fiber ends. In particular, the present invention relates to a tunable multiple optical fiber connector for tuning the core position of each fiber in the connector to optimize coupling efficiency.
In fibre based optical systems, signals propagate within optical fibres. When optically coupling two components, a fiber is coupled at a first end to a first component and at a second end to a second component. Often in an optical system, a plurality of fibres is routed within the system. When a large number of fibres are used, designs often incorporate cables comprising a number of fibres and having a single connector at each end of the cable. The single multi-fibre connector is provided with bores for accepting optical fibres. Into each bore, a fiber is inserted and held in place. Unfortunately, the bores are not always precisely located and, in order to insert a fibre, the bores must be larger in diameter than the outside diameter of the fibres in order to accommodate the fibres.
Small irregularities in ferrule and fibre manufacture can result in significant signal loss, particularly in coupling single mode fibres. A standard ferrule has an internal diameter closely matching a fibre diameter. However, a ferrule having for example an internal diameter of 128 xcexcm provided with a fibre having a diameter of 127 xcexcm may be placed up to 0.5 xcexcm from the concentric axis, equalling a total possible eccentricity of the optical fibre of 1 xcexcm. In addition, the bore of the ferrule in manufacture may not be concentrically placed. Tuning is thus necessary to optimize the position of the fibre ends within a connector and thereby adjust the coupling efficiency. For example, a simple tuning apparatus allows for insertion of a connector in any of a plurality of orientations. Once inserted, the connector is fixed in its orientation and, therefore, the coupling efficiency remains substantially constant and is improved when coupling is between two ends having similar orientations.
Unfortunately, when using cables comprising multiple fibres, each fibre coupling may result in significant loss. Tuning of fibres by moving the two connector ends does not result in each fibre pair being independently tunable. The relative placement of the connector ends cannot be reoriented because the fibre connections would change. When different fibres within a cable have alignment errors as is commonly noted, it is near impossible to find two connectors that couple efficiently for all fibre pairs. For example, when correct alignment is sufficiently approximated by aligning the connectors in one of four orientations, there is a one in four chance of a good coupling. Through tuning of a single fibre connector, the coupling is easily altered to achieve a most efficient coupling from the four available orientations. When two fibres are incorporated into a cable, there are 16 possible orientations and since tuning is not available, only one in 16 connectors provides good coupling with an existing connector. When a cable having 32 fibres is used, the chance of finding two that mate with reasonable coupling efficiency is very small.
For more efficient installation of multi fiber or ribbon fibres the coupling of multiple fibre ends at a single multi-fibre-connector pair, heretofore, has not been satisfactory. U.S. Pat. No. 5,671,311 to Stillie et al. discloses a method of aligning a number of receiving ferrules within a less precise housing by providing aligning pins for locating the ferrule bores in the housing. Once the ferrules are positioned the fibres are then inserted. This is a rather imprecise method, which does not provide an opportunity to correct transmission problems once the fibres and light sources are in place. Also, since the fibre is inserted after the tuning is performed, slack between the ferrule and the fibre can be a significant problem.
Alternative multiple fibre connectors are disclosed in U.S. Pat. No. 5,430,819 to Sizer II et al. A first connector manufactured by ATandT under the trademark MACII, secures a plurality of exposed fibre ends between a pair of silicon wafers having a groove precision etched to locate each fibre end. A second connector in accordance with the invention of Sizer II et al. provides a pair of substrate plates having fibre-sized holes etched through the substrate for locating each fibre end. Both of these methods require absolutely precise manufacturing at considerable cost, since no tuning adjustment of individual fibres is possible.
Tuning of single optical fibre connectors is known. For example, it is known to provide a keying mechanism on an optical fibre connector to prevent rotation of the optical fibre cable once a desired coupling position has been determined, as described in U.S. Pat. No. 5,096,276 to Gerace et al. The key element may be an asymmetric shape or a pin or the like in a push-pull plug type connector.
Two fibre ends joined in a connector may each be supported in a ferrule or similar housing. Most commonly a cylindrical ferrule with a central bore substantially the diameter of the exposed fibre is used to support the fibre end within the connector. As recognized in U.S. Pat. No. 4,738,508 to Palmquist, and also in U.S. Pat. No. 5,390,269 to Palacek et al., tuning of the ferrules within the connector is also needed to achieve high performance connection with low insertion loss.
Palacek and Palmquist propose providing multiple rotatable orientations of a fibre and ferrule within the connector by placing the ferrule within a housing or collar having facets or knurls for mating with a receiving housing.
It is an object of the invention to provide a connector for receiving and connecting multiple optical fibre ends, in which each optical fibre core is oriented in a predetermined fashion with respect to a key element of a connector housing.
Accordingly, the present invention related to a tuned multiple fibre optic connector for connecting a first plurality of optical fibre ends to a second plurality of optical fibre ends, each fibre end having an eccentrically positioned core therein, comprising:
a first connector housing comprising a first key element, the first connector housing for retaining each of the first plurality of optical fibre ends, the core of each of the first plurality of optical fibre ends oriented with respect to the first key element in a predetermined azimuthal fashion in a plane perpendicular to the longitudinal axis of the fibre; and
first coupling means for coupling the first connector housing to another connector housing.
Another aspect of the present invention relates to a tuned multiple fibre optic connector for connecting a first plurality of optical fibre ends to a second plurality of optical fibre ends, each fibre having an eccentrically positioned core therein, comprising:
a first plurality of optical fibre ends, wherein each optical fibre end is retained in a ferrule having at least an indicator element such that a core of the optical fibre end is oriented in a plane perpendicular to the longitudinal axis of the fibre, the orientation in a predetermined azimuthal fashion with respect to an indicator element of the ferrule; a first connector housing comprising a first key element, the first connector housing for retaining each of the first plurality of optical fibre ends in a predetermined location such that the indicator elements of the ferrules are disposed in a predetermined azimuthal relation to the first key element of the first connector housing; and first coupling means for coupling the first connector housing to another connector housing.